The present invention relates generally to microwave cooking appliances and more particularly to microwave cooking wherein microwave energy may be fed at any power ratio between a plurality of waveguides.
A problem of long standing in microwave oven appliances has been the distribution of microwave energy in the cooking cavity with respect to the type and size of food being cooked. For example with a large item to be cooked, such as a roast, it is desirable to heat both the top and bottom for best results, while for a relatively thin item to be cooked, such as bacon, the heating is more efficient with heat only on the bottom.
In an effort to alleviate the problem of microwave energy distribution, a great many approaches have been tried. One such approach in ovens having at least two waveguides fed from a single source of microwave energy is to provide a bifurcator which operates to provide a stable power split between the waveguides. Generally, this arrangement provides a fixed ratio or power split between the waveguides. While this arrangement provides satisfactory cooking results for the cooking requirements of most foods, it does not provide optimum heating or cooking for all types and sizes of food being cooked.
Another approach to the problem of microwave energy distribution is disclosed in U.S. Pat. No. 2,909,635 wherein a microwave oven with multiple cavities in which food masses of different sizes or different temperature characteristics can be placed. Multiple waveguides are used to supply microwave energy from a single source to each cavity so that simultaneous heating of such food masses results. A mode shifting device located at a common junction point of the multiple feed is also used to provide a uniform distribution of microwave energy for uniform heating of the food masses.
It is, therefore, an object of the present invention to provide in a microwave oven optimum cooking of foods having both large and small areas or volumes without excessive heating of food having smaller masses, or insufficient heating of food having larger masses.